This proposal is for the continuation of an existing collaborative program that employs engineering techniques to better understand the mechanism of lens accommodation and its age-related changes leading to presbyopia. The general application of these bioengineering studies is the development and testing of suitable devices or surgical procedures for the restoration of true dynamic accommodation in presbyopes. This continuation proposes to apply a lens stretching system and numerical finite-element biomechanical model developed in the previous grant period to investigate specific age-related changes in the human and monkey lens and their impact on the feasibility of procedures to restore accommodation. There are four specific aims: Aim 1: To validate the lens stretcher for studies on human and monkey lenses Aim 2: To enhance and validate the biomechanical model for studies on human and monkey lenses Aim 3: To quantify the role of the age-related changes in lens shape and internal structure on the amplitude of accommodation in human and monkey lenses. Aim 4: To quantify the role of zonular architecture and tension on accommodation in human and monkey lenses. A lens stretching system and numerical finite-element model developed to characterize the optomechanical response of post-mortem lenses will be calibrated by comparison with published optical and biometric measurements obtained in live human and monkey eyes. The lens stretcher and biomechanical model will be used to determine the respective contribution of age related changes in lens shape and internal structure on the loss of accommodation with age, as well as the role of the zonular architecture. The results of the studies will be incorporated in a refined numerical finite- element optomechanical model of accommodation and presbyopia that will be used to simulate the effect of age-related changes on the biometric and optical response of the lens during accommodation, as well as the effect of surgical techniques to restore accommodation. t Relevance to Public Health: Presbyopia is the age-related gradual loss of the ability of the eye to focus on near objects. The percentage of presbyopes (age 45 and above) in the US population is predicted to reach 40% by 2011. Biomedical strategies that can restore accommodation will significantly improve the quality of life for these physically and socially active members of our society. This project seeks to improve our understanding of age-related changes in the eye leading to presbyopia and to test approaches to correct presbyopia.